In analog integrated circuits, resistance elements are frequently used as important elements. Recently, a resistance element formed by a metal thin film (hereinafter “metal thin film resistance element”) in the resistance elements has attracted attention because the metal thin film resistance element has a low TCR (temperature coefficient of resistance) of a resistance value. For example, chrome silicon (CRSI), nickel chrome (NICR), tantalum nitride (TAN), chrome silicide (CRSI2), chrome silicide nitride (CRSIN), chrome silicon oxide (CRSI0), or the like is used as a material of the metal thin film resistance element.
In a semiconductor device having the metal thin film resistance element, in order to meet the demand of high integration, the metal thin film resistance element may be frequently formed by a thin film having a thickness equal to or less than 100 nm (1000 Å) so that a high sheet resistance is obtained.
In the related art, as a method for making electric connection of such a metal thin film resistance element, a method whereby a wiring pattern is formed on a lower layer side insulation film; a base insulation film is formed on the wiring pattern; a connection hole is formed in the base insulation film on the wiring patter; and the metal thin film resistance element is formed in the connection hole and on the base insulation film, has been used. See, for example, Japanese Laid-Open Patent Application Publication No. 2002-124639.
A related art semiconductor device is discussed with reference to FIG. 1 and FIG. 2. Here, FIG. 1 is a view showing the related art semiconductor device, more specifically, FIG. 1(A) is a plan view of the related art semiconductor device; FIG. 1(B) is a cross-sectional view taken along a line A-A of FIG. 1(A); and FIG. 1(C) is a cross-sectional view taken along a line B-B of FIG. 1(A). FIG. 2 is an equivalent circuit of FIG. 1(A).
Referring to FIG. 1 and FIG. 2, an interlayer insulation layer 5 is formed on an element isolation oxide film 3 formed on a silicon substrate 1. A metal wiring pattern 7 is formed on the interlayer insulation layer 5. A base insulation film 9 is formed on an entire surface of the interlayer insulation layer 5 including the metal wiring pattern 7.
A connection hole 45 is formed in the base insulation film 9 on the metal wiring pattern 7. A metal thin film resistance element 47 is formed on the base insulation film 9 including a forming area of the connection hole 45.
A passivation film 15 is formed on the base insulation film 9 including a forming area of the metal thin film resistance element 47 as a final protection film.
As shown in FIG. 1(B), a lower surface of the metal thin film resistance 47 is electrically connected to the metal wiring pattern 7 in the connection hole 45.
In addition, as shown in FIG. 1(A), plural metal thin film resistance elements 47 are connected in series via the metal wiring patterns 7.
The metal thin film resistance elements 47 form a unit resistance. This unit resistance is prepared in various connection ways such as a block of a series connection or a parallel connection of one metal thin film resistance element, two metal thin film resistance elements, four metal thin film resistance elements, eight metal thin film resistance elements, sixteen metal thin film resistance elements, thirty two metal thin film resistance elements, sixty four metal thin film resistance element and so on. A single or plural of these blocks are connected so that a splitting resistance circuit or the like necessary for the circuit is formed.
In the examples shown in FIG. 1 and FIG. 2, the metal thin film resistance elements 47 of a single resistance R1, two resistances R2, and four resistances R3 are connected in series and the resistances R1, R2, and R3 are connected in series. When a voltage is applied between electrodes A through D, voltages corresponding to a resistance ratio of electrodes B and C are output.
According to a connection method shown in FIG. 1, a substantial resistance value including resistance of an electrode per se, contact resistance of the electrode and the metal thin film resistance element, or the like substantially follows the number of the metal thin film resistance elements. Therefore, it is possible to easily design and avoid unevenness of resistance values.
Meanwhile, the analog integrated circuit requires a lay-out using a metal thin film resistance element having width as narrow as possible so that a large number of the metal thin film resistances are arranged. Therefore, the metal thin film resistance element is formed in an area close to the minimum resistance element pattern width that can be formed by a semiconductor process for manufacturing the analog integrated circuit.
However, in a case where a hole for connecting or an electrode is formed by the metal thin film resistance element whose lay-out is made in the vicinity of the minimum width, if a sufficient space of overlapping between the connection hole and the metal thin film resistance element is necessary, the connection hole may not be received in the width of a single metal thin film resistance element due to the size of the connection hole formed by a minimum size of the same process rule.
There are generally two methods as discussed below to correspond to this case.
(1) Only the connection hole forming part of the metal thin film resistance element is made wide.
(2) As shown in FIG. 3, the structure where a single metal thin film resistance element 47 is connected as the unit resistance is not applied, but a meandering metal thin film resistance element is formed by connecting two belt shape parts 47a with a turning part 47b, and a connection hole 45a and the metal wiring pattern 7 are arranged under the turning part 47b. Here, FIG. 3 is a plan view showing another related art semiconductor device.
In the case of the above-mentioned (1), since the metal thin film resistance element of the connection hole part is wide, the area of the lay-out of the metal thin film resistance element is increased.
On the other hand, in the case of the above-mentioned (2), since the connection hole 45a is arranged under the turning part 47b connected to two belt shape parts 47a, it is possible to make the connection hole 45a larger than the width of the belt shape part 47a without increasing the lay-out area.
In addition, since the connection hole 45a and the metal wiring pattern 7 are provided at both ends of a single belt shape part 47a, the resistance values corresponding to the number of the belt shape parts 47a may be easily obtained.
However, in the lay-out of the above-mentioned (2), as shown by an arrow in FIG. 3, at the turning part 47b of the metal thin film resistance element, the electrical current flows not to the connection hole 45a or the metal wiring pattern 7 but via an overlapping space part. For example, at extended parts such as the electrodes A through D, an electric current flows via the connection hole and the electrode part and therefore a designated resistance value or resistance ratio is not obtained. Such a problem may occur more frequently as the number of the belt shape part 47a and the turning part 47b connected in series is increased.